The present invention relates to a centrifugal separation device and method of separating solids in liquids. The liquid has solid particles in suspension. Suspended solids removal can be achieved in many ways. Solids can be settled out in a tank, filtered out using cartridges or indexing paper or a filter press. Settling is a slow process and other alternatives generate an immense labor cost or a waste stream that may be greater than the solids alone.
Use of a centrifugal separation device allows the extraction of the solid particles from the liquid. In a centrifugal separator, the separation of the solid from the liquid is commonly accomplished by pumping the contaminated liquid or coolant into a high speed rotating chamber or bowl. The centrifugal forces created by high speed rotation of the chamber cause the contaminated fluid to conform to the interior surface of the rotating chamber. The centrifugal energy causes the heavier solids to concentrate in a solid cake form for easy removal, reclamation, reuse or disposal. Since the chamber or bowl is rotating at a high speed, the solid material adheres to the side of the bowl while a cleansed coolant or liquid exits through an opening or openings commonly located at the bottom or top of the bowl. Centrifugal separation is preferable to the more traditional medium of filtration because filtration does not allow for removal of submicron particles without extensive and very expensive filtering. When such filtering is performed, the filter paper or cartridges become clogged quickly and must be disposed of. Additionally, these filtration devices often cannot pass high viscosity fluid.
With the advent of computer controls, the horizon of activities to which centrifugal separation may be applied, such as use as a waste separator, has been greatly expanded. For example, metal working coolants often become contaminated during grinding, wire drawing, machining, polishing, vibratory deburring or other metal working processes. Centrifugal separation allows fluid cleaning to increase coolant life and the solid discharge from centrifugation may have a marketable value or be disposable at minimal costs. The large spectrum of applications extends to contaminated fluids resulting from phosphate baths, dielectrics, glass grinding, EDM machining, water rinse baths, acid baths, all the way to food processing wherein oils can be contaminated by starches and other food products.
It is well known in the art that the efficiency of a centrifugal separator decreases when the scraper blades or stilling vanes do not rotate at the same speed as the bowl or chamber. It is desirable if the scraper blades inside the bowl rotate at the same speed as the bowl until such time as it is desired for them to scrape or plow the solids from the side of the bowl and expel them from the process chamber.
Current systems, as will be discussed in more detail later, use a frictional mechanism in an attempt to obtain equal rotational speeds between the blades and the bowl. This frictional mechanism does not provide the consistent synchronous blade and bowl rotation desired. In operation, a user will periodically start the system up and direct a strobe light into the centrifuge to check whether the bowl and blade are rotating at the same speed. Since the frictional mechanism does not provide a positive lock between the bowl and the blade there is no way of knowing whether the bowl and blade are continuing to rotate together during processing. Furthermore, the frictional clutch mechanism possesses a great many parts, which increases the amount of time that must be spent for maintenance purposes.
Additionally, current systems are prone to spray or mist the fluids exiting the rotating bowl, which can be hazardous to human occupants in the room where centrifugation is occurring. Also, this spray or mist can collect and cause dripping which coats the centrifuge or surrounding machinery, and may contaminate the solids expelled from the centrifuge into a waiting receptacle.
Another difficulty encountered is that some sticky solids refuse to let go of the blade during scraping. Different geometries are preferable to get the solid to peel off. However, each blade must be balanced to reduce vibration of the system, and it is expensive to produce and balance each blade properly. It would be advantageous if individual blades could be customized with different geometries for use in different applications. Other difficulties encountered with current blade designs are that they generally require a large amount of torque to operate. The application of large torque can sometimes result in the blade drive shaft breaking. Current blade designs also often possess a large surface area to which solids may stick. Designs in which the surface area is minimized while retaining equally effective scraping capacity and stilling action are desirable.
Other problems with centrifugal separation include difficulties in accurate measurement of the flow of contaminated liquid into the system. Since the liquid is contaminated with solid particles accurate measurement of the flow rate into the centrifuge is difficult and often requires the use of expensive equipment.
The present invention meets the demand for a coupling mechanism ensuring synchronous blade and bowl rotation in the centrifuge. Additionally, it minimizes the occurrence of spray and misting upon exit from the apparatus. Furthermore, it provides a solution to the problem of obtaining variable geometries using a standard blade with inserts. Also disclosed are blade designs for minimizing the torque required to operate the system as well as minimizing the surface area to which solids may stick while retaining effective scraping and stilling ability. A simple method for measuring flow is also disclosed along with a method for cleaning the blades of solids stuck thereon.
In one aspect of the invention the centrifuge comprises a spindle centered on a longitudinal axis with a top portion, a bottom portion, and a hollow interior extending along the longitudinal axis, a bowl attached to the bottom portion of the spindle and a drive shaft passing through the hollow interior with a plurality of scraper blades attached to the drive shaft. The centrifuge has a clutch mechanism comprising a shifting coupling attached to the blade drive shaft via a key locked in a rotary direction. The shifting coupling has a first set of teeth that interlockingly engage a second set of teeth. The second set of teeth are attached to the top of the spindle in one embodiment. In another embodiment the second set of teeth are attached to a pulley attached to the top portion of the spindle. The shifting coupling may be shifted upward and downward along the longitudinal axis between two positions. In the first position the first and second set of teeth are lockingly engaged so that the spindle and the scraper drive shaft rotate together. In the second position the first and second sets of teeth are disengaged.
In another aspect of this invention the centrifuge comprises a spindle configured to rotate about an axis. A bowl is attached to and rotates with the spindle. A drive shaft is received within a passageway of the spindle and rotates about the same axis. A scraper blade is attached to and rotates with the drive shaft. A mechanism is provided to selectively couple the drive shaft and spindle together to allow both to be driven by the same motor.
In another aspect of this invention the centrifuge scraping apparatus comprises blades with recesses on its front face adjacent the end of the blade next to the inner surface of the bowl. Inserts are placed in the recesses to give the scraper blade different cutting surfaces for contacting solids accumulated on the interior wall of the bowl.
In another aspect of the invention the centrifuge scraping kit comprises a rotatable scraper frame with a number of opposing ends. Each of the ends is adjacent the interior wall of the bowl and is also adjacent a front face of a blade in which a number of recesses are defined. A set of scraper inserts configured to plow solids accumulated on the interior wall of the bowl are placed in the recesses.
In another aspect of the invention the centrifuge comprises a housing with a rotatable bowl therein. The housing is cylindrical with a closed top end and an at least partially open bottom end. The housing has a tangential outlet which minimizes the entrainment of gas by a liquid exiting the bowl during processing.
In another aspect of the invention the centrifuge comprises a spindle attached to a bowl which rotate together. The centrifuge has a drive shaft which is received in a passageway defined by the spindle. The drive shaft is attached to scraper blades which rotate with the drive shaft. The centrifuge has means for selectively rotating the drive shaft and spindle together.
In another aspect of the invention, the centrifuge apparatus comprises a first scraping blade and a second scraping blade which rotate around a longitudinal axis. The first blade has a first forward face and a first rear face, each of the faces extend between a first radially inner edge which is located substantially along a first inner radius from the axis and a first radially outer edge located substantially along a first outer radius from the axis. The second blade has a second forward face and a second rear face, each of the faces extends between a second radially inner edge located substantially along a second inner radius and a second radially outer edge located substantially along a second outer radius. The first outer radius and second inner radius are such that the first and the second blades have at least some radial overlap.
In another aspect of this invention the centrifuge scraper blade assembly comprises a first and second pair of centrifuge blades which rotate around a longitudinal axis. The first pair of blades are substantially symmetrical around the longitudinal axis. Each of the blades of the first pair of blades has a radially inner edge substantially along a first radius and a radially outer edge substantially along a second radius. The second pair of blades are substantially symmetrical around the longitudinal axis, each of the blades of the second pair of blades has a radially inner edge substantially along a third radius and a radially outer edge substantially along a fourth radius. The second radius is at least equal to the third radius and the second radius is smaller than the fourth radius.
In another aspect of this invention the centrifuge apparatus comprises a plurality of scraping blades rotating around a longitudinal axis, each of the blades has a scraping face and a trailing face, and each face has a top edge, a bottom edge, an inner edge and an outer edge. At least the first portion of each blade radially overlaps at least a second portion of another of the plurality of blades.
Another aspect of the invention comprises a method of determining flow rate into a rotor assembly which has an accelerator, a drive motor, and a plurality of stilling vanes which comprises the steps of accelerating the rotor to speed, maintaining the rotor at speed and measuring a first baseline value of load. Additional steps include injecting a fluid into the rotor assembly, maintaining the rotor at speed while accelerating the fluid in the rotor assembly, and using a programmable logic controller to subtract the first value from the second value to obtain a third value. The third value is converted by the programmable logic controller into a flow rate of the fluid being injected into the rotor assembly.
In another aspect of this invention the centrifuge apparatus comprises a centrifuge having a plurality of scraping blades rotating around a longitudinal axis. Each of the blades has a scraping face and a trailing face, the faces having a top edge and a bottom edge and an inner edge and an outer edge. At least one of the blades is angled to force the solids toward a discharge opening in the centrifuge.